Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
t
~ackground of the Inventlon
F'ield o~ the Invention
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This invention is in the field of permanent magnet
holding pla-tes. A primary use i5 as a magnetic holding
saddle for a printing press roll or cylinder for holding
a flexible, steel-backed printing plate in place dur.ing
the printing operation..
Description of the Prior Art
A prior art magnetic cylinder or saddle for a print-
ing press is disclosed in U.S. Patent 3,810,055 issued
May 7, 1974 to Theodore D. Wright. Although the '055
device can be used for other purposes, it is primarily for
use as a magnetic holding device to hold a flex.ible or
curved steel-backed printing plate without the need for
mechanical clamps or the like which had been necessary in ~ ~
the past. The device described in the '055 patent is con~
structed by spiraling a pair of elongated strips of flexible
permanent magn.ets in a pair of parallel spiraling grooves
around a cylinder. Between the magnet strips are strips
of magnetic material and the permanent magnets induce mag-
netic poles into the magnetic material strips so they become
pole pieces and concentrate the magnetic lines of force~:
near the surface of the cylinder to create a strong~;
magnetic holding force to hold the printing plate in place
on the cylinder. Another device which finds its principal
use as a magnetic holder for a printing plate is shown in ~:
U.S. Patent 3,824,927 issued July 23, 1974 to Pugh et al. ~ .
Here the magnetic holding device is formed by a sheet or
~layer of magnetic rubber placed over a curved steel
supporting layer.
While both oE the aforementioned devices may work
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well and may be meritoriou~, th~y do have cert~in limitations.
One difficulty with the '055 ~evice i8 the problem of
making the spirally-wrapped cylinder into a saddle by cut- :
ting the cylinder into sections. Another difficulty is
the problem that sometimes occurs in assemblying the device
in handling the long strips of flexible permanent magnets
to arrange them in the slots. Also, there can be some
difficulty in ensuring intimate contact between the flexible
magnet strips and the adjacent rigid pole pieces to reduce
magnetic field loss. Another disadvantage of the '055 mag-
netic holder is that because of the way it is constructed,
it cannot be made thin enough to be used in certain
applications.
The '927 device, without pole pieces, would appear
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to have insufficient mechanical strength and magnetic
holding power so would need auxiliary means for holding
the printing plate in place, and is not too durable
because the layer of flexible magnet material is located
unprotected on the outer surface of the cylinder or
saddle. This makes it susceptible to damage during use
and handling.
Summary of the Invention
According to one aspect of the invention there is
provided a magnetic device for holding a printing plate
comprising- a base plate made of rigid, substantially
non-magnetic material, said base plate exhibiting an
arcuately curved outer surface, a plurality of spaced-
apart rigid strips of magnetic material arranged at the
outer surface of the base plate and extending transverse
to the direction of curvature of said base plate, and
compressible magnet-strips located in respective spaces
between said rigid strips, said compressible magnet strips
making intimate side-to-side contact with their adjacent
rigid strips and being arranged so that the same magnetic
pole is located at opposite sides of each alternate rigid ~`
strip to form successive rigid strips into magnetically
induced pole pieces of opposite polarity, wherein said
compressible magnet strips and said rigid strips are
disposed and configured on said base plate to effect
a greater magnetic field concentration in respective
areas of said device which in use are engageable with
end portions of the printing plate than in areas inter- ~
mediate said end portions of the printing plate. ~`
According to another aspect of the invention there is
provided a magnetic device for holding a printing plate
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comprising: a base plate made of rigid, substantlally
non-magnetic material, said base plate exhibiting an
arcuately curved outer surface, a plurality of spaced-
apart magnetic strips of magnetic material aranged at
the outer surface oE the base plate, and compressible
magnet strips located in respective spaces between said
magnetic strips, said compressible magnet strips making
intimate side-to-side contact with their adjacent magnetic
strips and being arranged so that the same magnetic pole
is located at opposite sides of each alternate magnetic
strip to form successive magnetic strips into magnetically
induced pole pieces of opposite polarity, wherein said
compressible magnet strips and said magnetic strips are
configured on said base plate to effect a greater mag-
netic field concentration in respective areas of said
device which in-use are engageable with end portions of
the printing plate than in areas intermediate said end
portions of tl~e printing plate.
Other aspects of this invention are protected in a
divisional application.
Brief Description of the Drawings
Fig. 1 is a perspective view of a permanent magnet
saddle for a printing cylinder constructed according to
the teachings of this invention;
Fig. 2 is a partial section taken parallel to the line
oE curvature of the saddle; and
Fig. 3 is a partial section taken along a line
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transverse -to the line of curvature oE the saddle.
Description of the Pre~e.rred Embodiments
Referring to the drawings, the curved, permanent
magnet saddle lO has a base plate 11 made out of a thin but
sti~f sheet of nonmagnetic material which, fox example, might
be aluminum or some other material suitable to provide the
necessary base support. Along each side of magnetic saddle
10 is a side rail 12 which runs along the line of curvature
for the entire curved length of the saddle. The side rails
12 are preferably made out of the same material as the base .
plate but need not be, although they too should be made out
of a suitable nonmagnetic material. Extending across the ~ :
top surface of the base plate 11 from side rail to side rail ; ~:
are a series of strips of ferromagnetic material 13. As will .~ :
become evident later, these strips are referred to as pole
pieces. The pole pieces are laid out generally parallel to
one another and are spaced apart over the length of the base ~ .
pla~e. As can be observed most clearly in Fig. 3, the pole
pieces 13 are located and held in place by virtue of shoulders ;~.: ;
14 formed on each end of each pole piece 13 engaged in recesses
15 on the inner lower side of the side rails 12. Also located ~
on the top surface of the base plate 11 and in the spaces ~ `
between successive pole pieces 13 are strips o~ flexible,
permanent magnet material 16. The preferred material for
the magnet strips 16 is a rubber bonded barium ferrite composite ;.
material which is known commercially under the registered trade~
mark name of "PLASTIFORM" and is made by Minnesota ~ining and ...
ManuEacturing Company. This material has the characteristic
o~ being flexible enough to be bent or twisted or wound in .
a variety of shapes or forms and is compressible to some
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degree and consists of a rubber base~ matrix or binder
containing powdered ferrite particles which are mechanically
orientated during processing and aligned and held to consti-
tute a good permanent magnet. Because a flexible permanent
magnet material is used, it lends itself to certain advan-
tages because the strips can be inser-ted between successive :
pole pieces and be compressed against the pole pieces to :~
make intimate contact with the pole pieces so as to lessen
any magnetic loss. The permanent magnet strips 16 are polarized
so that successive strips have the same pole on opposite sides ~ ;
of the pole piece between them, as best observed in Fig. 2. - .
In this manner successive pole pieces have magnetic poles ~ ~:
o~ opposite polarity induced in them so that the magnetic ~. :
lines leaving one pole piece are directed to a next successive
pole piece in both directions and tend to concentrate close .. ;
to the surface of the saddle 10. At each end of base plate
11 is a head piece 17 and a tail piece 18 which serve to
lock the pole pieces and the magnetic strips within the confines ~ :
of the saddle.
The device is preferably assembled by first attach-
ing the tail piece 18 or the head piece 17 to one end of
the base plate 11 and then inserting each pole piece 13 by ~ :
placing the shoulders 14 in the recess 15 of side rails 12 .;
and placing a magnet strip I6 between each of the pole pieces. .
Pressure can then be applied, in some suitable fashion, length-
wise of the saddle to the sides of a group of assembled pole
pieces and magnet strips to compress the latter firmly between
successive pole pieces and thereby assure good intimate con- : .
tact between the pole pieces 13 and the adjacent magnet
strips 16. Although the pole pieces can then be secured in
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position in a variety of ~ashions, it is preferred that
a suitable adhesive be applied to the ends o~ the pol~
pieces to make sure they do not work loose when the completed
saddle is in use.
A feature of this invention is that the underside
o~ the base plate can be machined if necessary to ~orm a
slot or recess in order to mechanically attach the saddle
to a printing press cylinder roll that uses a tension lockup
mechanism. This make it interchangeable with other print~
ing press saddles without altering the mechanism for latching
the saddle to the cylinder. Similarly, the side rails 12 can
be beveled if necessary for use on a printing press cylinder
where the printing press cylinder has a standard compression
lockup device. In other words, the permanent magnetic saddle
constructed as taught by the instant invention can easily be
adapted for use with traditional printing devices.
Because of the nature of the construction of this
device, a concentrated magnetic field can be achieved to
produce the magnetic holding strength necessary for the
intended purpose yet the saddle can be made quite thin. This
is an advantage because then the saddle can be used within ~;
the dimensional limits of the printing machines~ In the
past, the steel-backed printing plate (which replaced the
stereotype or electrotype cast lead plate) was mechanically
locked onto a printing saddle. This invention holds the
s-teel-backed printing plate with the required holding strength
yet can be made within the permissible thickness dimension
~or the saddle. In this way the location and dimensions of -
the printing rolls or cylinders need not be altered to
~0 accommodate the magnet saddle 10.
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While the instant embodiment illus-trate~ the pole
pieces 13 and permanent magnet strips 16 covering the entire
length and breadth of the saddle 10, i-t has been found that
in some instances a printing plate can be securely held in
position by having pole pieces and permanent magnet strips
only at the tail and front ends of the saddle. This will
depend upon the particular application and the degree of
holding strength necessary to keep the printing plate in
place during the prin-ting operation.
It has also been found that the permanent magnet
strips 16 can be slightly tapered along their sides to
ensure good intimate contact with the adjacent pole pieces
13. Also, in some cases the permanent magnet strips 16 and ~-
pole pieces 13 near the head and tail ends of the saddle may
be somewhat thinner than in the central area of the saddle
so there would be a greater magnetic field concentration in -
those end areas where a stronger magnetic holding strength
may be necessary or desired.
Although the preferred embodiment is shown and
described as being arcuate in -form, the holding device,
for some applications, may be made flat, yet will retain all
oE the benefits, features and advantages.
A further feature of this invention is that the
magnetic field of the holding plate can be arranged and
directed so as to provide the means for attaching it to
-the printing press cylinder, provided the latter is made
out of a suitable magnetic material. In other words, the
magnetic field can serve a twofold purpose, one being to
hold the plate to the printing press cylinder and the other `
~0 being to hold the steel backed printing plate, and thereby
eliminate the need for mechanical locking devices.
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